Exploring Bemisia tabaci Middle East-Asia Minor I and Mediterranean Cryptic Species Relationship with Cowpea Mild Mottle Virus and Their Dynamics in Soybean Fields.

Cowpea mild mottle virus (CPMMV, genus Carlavirus, family Betaflexividae) is an economically important virus infecting soybeans in Brazil, where it was initially identified in 1983. CPMMV is transmitted by the whitefly, Bemisia tabaci, and occasionally by seeds. Over the last three decades, the most invasive B. tabaci Middle East-Asia Minor 1 (MEAM1), and lately the Mediterranean (MED) cryptic species, have replaced the indigenous species in Brazil, with MEAM1 being predominant. In this study, we investigated the transmission properties of CPMMV by MEAM1 and MED, and their distribution in major soybean-growing areas in São Paulo State. Our results from transmission assays with a single insect revealed that MED is a more efficient vector compared to MEAM1, transmitting the virus within a two-minute inoculation access period. B. tabaci MEAM1 is still the predominant whitefly species in São Paulo State, but MED was also identified in different places, mainly in mixed infestations with MEAM1. Some areas transitioned to a predominance of MED over the three years, while others, where MED had previously been detected, showed a reduction in the insects during the same period. Understanding the transmission dynamics of CPMMV and the distribution of its vectors is crucial for implementing effective management strategies to control the virus spread and protect soybean crops. Further research into the mechanisms driving the shifts in whitefly species dominance and CPMMV distribution will be essential for sustaining soybean production in Brazil.

Monitoring the susceptibility of Bemisia tabaci Middle East-Asia Minor 1 (Hemiptera: Aleyrodidae) to afidopyropen, cyantraniliprole, dinotefuran, and flupyradifurone in south Florida vegetable fields.

Bemisia tabaci Middle East-Asia Minor 1 (MEAM1) is a significant pest that damages a wide range of high-value vegetable crops in south Florida. This pest has demonstrated the ability to develop resistance to various insecticide groups worldwide. Monitoring the resistance levels of MEAM1 populations and maintaining baseline susceptibility data are crucial for the long-term effectiveness of insecticide management strategies. We conducted serial dilution bioassays on 15 field populations of MEAM1 collected in south Florida to assess their resistance to 4 key insecticides: afidopyropen, cyantraniliprole, dinotefuran, and flupyradifurone. To quantify resistance levels, resistance ratios (RR) were generated by comparing the LC50 values of field populations to those of a known susceptible MEAM1 colony reared in the laboratory. Our findings reveal that all field-collected populations were susceptible to dinotefuran (RR 1-8) and flupyradifurone (RR 2-8). While over 80% of the populations tested were susceptible to afidopyropen (RR 1-9), 2 populations exhibited low (RR 38) and moderate resistance (RR 51), respectively. In contrast, most of the populations (57%) showed low to moderate resistance to cyantraniliprole (RR 21-78), and the remaining populations were susceptible (RR 3-10). The 2 populations with resistance to afidopyropen also exhibited moderate resistance to cyantraniliprole. Further research in this direction can aid in refining insecticide resistance management programs in Florida and other regions where B. tabaci MEAM1 is a major pest. Exploring the implications of these findings will be essential for insecticide use and integrated pest management strategies in south Florida.

Molecular and biological characterization of an isolate of the potyvirus passiflora virus Y naturally infecting soybean (Glycine max) in Brazil.

Passiflora virus Y was detected naturally infecting soybean (Glycine max) for the first time in Brazil. Here, we report the nearly complete genome sequence and molecular and biological properties of the PaVY-Br isolate. The nearly complete genome sequence is 9679 nt long and shares 84.4% nt sequence identity with a previously reported PaVY isolate from Passiflora sp. PaVY-Br induced chlorotic spots and systemic mosaic on soybean and chlorotic local lesions on yellow passion fruit (Passiflora edulis) and sesame (Sesamum indicum). The virus was successfully transmitted by Myzus persicae, indicating that this aphid vector can contribute to the spread of PaYV from passion fruit to soybean plants. Additional epidemiological research is in progress to investigate the distribution of PaVY in soybean production areas in Brazil.

Effects of cowpea mild mottle virus on soybean cultivars in Brazil.

Soybean stem necrosis is caused by cowpea mild mottle virus (CPMMV), transmitted by the whitefly Bemisia tabaci. CPMMV has already been recorded in all major soybean-producing areas of Brazil. The impacts caused by CPMMV to the current Brazilian soybean production are unknown, thus the main objective of this study was to evaluate the effects of CPMMV infection on the main important soybean cultivars grown in the Southern and Midwestern regions of Brazil. Although asymptomatic in some of the tested cultivars, CPMMV infection significantly reduced the plant height, the number of pods per plant and the 1,000-grain weight. In addition, estimated yield losses ranged from 174 to 638 kg ha-1, depending on the cultivar. Evidence of seed transmission of CPMMV was observed in the BMX POTÊNCIA RR cultivar. These results suggest that CPMMV could have an important role in the reduction of soybean productivity in Brazil, but symptomless infections might be hiding the actual impact of this pathogen in commercial fields and infected seeds could be the primary inoculum source of the virus in the field.